Many data communications use specific clock frequencies. For example, time domain multiplexing/pulse code modulation (TDM/PCM) audio interface protocols typically use an 8.192 MHz PCM clock for an audio sampling rate of 8 KHz. The specific frequency is usually served by dividing an external crystal oscillator of a particular frequency by an integer number using a clock divider. For example, in TDM/PCM, input from an external crystal oscillator with a frequency of 49.152 MHz is divided by 6 in a device supporting the protocol to generate the 8.192 MHz PCM clock. However, the extra crystal oscillator and other components supporting the crystal oscillator may increase the cost and the size of the circuit board. Furthermore, in a system where a clock of a specific frequency needs to be synchronized with other clock sources, additional circuits may be needed to synchronize the oscillator.
It is thus desirable to derive a target clock with a specific frequency from other clock sources that have been used in the system already. However, in many cases, to generate the target clock with the desired frequency from existing clock sources used in the system, a non-integer dividing ratio may be required, which may be difficult or costly to implement.